DE102011008459A1 - Cable bushing for the boiler wall of an HVDC component - Google Patents

Abstract

The invention relates to a cable bushing for the boiler wall of a HVDC component. This has a passage element in the form of an electrode tube (25) or a conductor pin (23). This passage member is provided with a sheath (26) of a cellulosic material whose resistivity is reduced by a treatment according to the invention in comparison with cellulosic material without such treatment. In this way, a higher dielectric strength of the insulating section, formed from the sheath (26) and further solid barriers (28) can be achieved. The improved dielectric strength advantageously opens up additional design freedom for the passage.

Description

The invention relates to a cable bushing for the boiler wall of a HVDC component. This has either an electrode tube or a conductor pin, which has a conductive surface. This component, which will also be referred to below generally as a conducting element, is usually made of copper. As electrode tube, this passage can be set to potential, this electrode tube for shielding a HVDC line is used, which can be performed electrically isolated through the tube interior. If the passage element is designed as a conductor pin, it serves directly as a HVDC line. This is suitably contacted inside and outside the boiler with a HVDC line. In addition, the cable bushing on a sheath of a cellulose material, in particular paper, on. This is usually wrapped as a paper wrap around the electrode tube or the conductor bolt, so that this or this is fully enclosed.

A cable bushing of the type specified is, for example, according to the EP 285 895 A1 described. This cable bushing has a conductor bolt as a passage element. In addition, such a line implementation is also in the DE 10 2005 021 225 A1 described. This cable bushing is suitable for guiding a HVDC line through a correspondingly formed electrode tube. In any case, a wrapping of the passage element is provided with a cellulosic material, with this enclosure further solid barriers follow in the form of several concentrically arranged Presspanzylindern, which together with the enclosure result in an insulating section. Transformer oil is provided in the spaces between the individual solid barriers and the paper wrapper. This fills the interstices, with absorbent materials such as pressboard and absorb the transformer oil.

HVDC components in general are understood to mean those components which are used for the transmission of high-voltage direct currents and contain current-carrying elements (HVDC stands for high-voltage direct current transmission). In particular, transformers or chokes are required as HVDC components. However, cable routing for the electrical connection of various HVDC components are required. Further HVDC components are disconnection points in such cable guides or bushings through housing components in which other HVDC components are housed. In addition to leading to high-voltage direct currents occur, for example, in transformer and choke coils and alternating currents. The HVDC components in the context of this invention should be suitable for transmitting high-voltage direct currents of at least 100 KV, preferably for the transmission of high-voltage direct currents of more than 500 KV.

From the US 4,521,450 It is known that a impregnable solid material made of cellulose fibers in an aqueous oxidizing agent, such as. As a weakly acidic solution of iron (III) chloride solution, cerium (IV) sulfate, potassium hexacyanoferrate (III) or molybdatophosphoric acid can be immersed. Subsequently, the wet cellulosic material is treated with either liquid or vapor pyrrole compounds at room temperature until the pyrrole is polymerized depending on the concentration of the oxidizing agent. The thus impregnated cellulosic material is dried at room temperature for 24 hours. The oxidizing agent ensures on the one hand for the polymerization of the pyrrole compounds, in addition to an increase in electrical conductivity. The specific resistance ρ of such impregnated cellulosic materials can thus be influenced by the concentration of pyrroles and the type of oxidizing agent.

Furthermore, it is known that nanocomposites can also be used as a field grading material when it comes to reducing peaks in the formation of electric fields, for example on the insulation of electrical conductors. According to the WO 2004/038735 A1 For example, a material consisting of a polymer can be used for this purpose. In this, a filler is distributed whose particles are nanoparticles, so have a mean diameter of at most 100 nm. According to the US 2007/0199729 A1 For such nanoparticles, inter alia semiconducting materials can be used whose band gap lies in a range of 0 eV and 5 eV. By means of the used nanoparticles, which can for example consist of ZnO, the electrical resistance of the nanocomposite can be adjusted. If, during the admixture of the nanoparticles, a certain proportion of the volume is exceeded, which is between 10 and 20% by volume, depending on the size of the nanoparticles, the specific resistance of the nanocomposite is noticeably reduced, with the result that the electrical conductivity of the nanocomposite is adjusted and can be adapted to the required conditions. In particular, I can set a resistivity of the order of 10 ¹² Ωm. This results in a voltage drop across the nanocomposite, which results in a more uniform distribution of the potential and thus also grades the resulting electric field in a suitable manner. As a result, the resulting field peaks can be reduced, which advantageously increases the dielectric strength.

When the electrical conductor is subjected to an alternating voltage, a field-grading effect is also produced which, however, follows a different mechanism. The field-weakening effect of the nanocomposite depends on the permittivity of the nanocomposite, the permittivity ε being a measure of the permeability of a material for electric fields. The permittivity is also referred to as the dielectric constant, the term "permittivity" being used below. As the relative permittivity is referred to by the relative permittivity ε _r = ε / ε ₀ designated ratio of the permittivity ε of the substance to the electric field constant ε _0, which indicates the permittivity of vacuum. The higher the relative permittivity, the greater the field weakening effect of the substance used in relation to the vacuum. In the following, only the permittivity figures of the substances used are dealt with.

The WO 2006/122736 A1 also describes a system of cellulosic fibers and nanotubes, preferably carbon nanotubes (hereinafter CNT), in which specific resistances of about 6 to 75 square meters can be set. These nanocomposites are to be used, for example, as electrical resistance heating, wherein the conductivity is designed with regard to an ability of the material of the conversion of electrical energy into heat. For this purpose, a sufficient degree of coverage of cellulose fibers with CNT is required.

The WO 2006/131011 A1 describes a socket, which may consist inter alia of an impregnated paper wrap.

As a material for impregnation, BN is also mentioned among other materials. This can also be used in doped form. In addition, the particles should be used with a concentration in the cellulose material below the percolation threshold, so that there is no electrical contact between the particles with each other. For this reason, the specific electrical resistance of the nanocomposite remains essentially unaffected.

From the application with the file number published after the date of this application DE 10 2010 041 630.4 For example, a nanocomposite comprising semiconducting or nonconducting nanoparticles dispersed in a cellulosic material such as pressboard is known, which can be used as a field grading material in transformers. At least part of the nanoparticles distributed in the cellulosic material have an enclosure of an electrically conductive polymer. As the cellulose material, for example, a paper, paperboard or pressboard can be used. The cellulosic material has a construction of cellulosic fibers which in their entirety make up the bandage forming the cellulosic material. Si, SiC, ZnO, BN, GaN, AlN or C, in particular also boron nitride nanotubes (hereinafter referred to as BNNT) can be used as semiconducting or nonconducting nanoparticles, for example. As electrically conductive polymers in the DE 10 2007 018 540 A1 mentioned polymers find use. Examples of electrically conductive polymers include polypyrroles, polyaniline, polythiophenes, polyparaphenylenes, polyparaphenylenevinylenes and derivatives of these polymers mentioned. A specific example of such polymers is PEDOT, which is also sold under the trade name Baytron by Bayer AG. PEDOT is also referred to by its systematic name as poly (3,4-ethylene dioxythiophene).

According to the filed with the file number after the date of this application DE 10 2010 041 635.5 It can also be provided that the impregnation consists of a polymer which is crosslinked from a negative ionomer, in particular PSS, and a positively charged ionomer. As positively charged ionomers preferably PEDOT or PANI can be used. PEDOT refers to the already mentioned poly (3,4-ethylene-dioxydthiophene). PANI is polyaniline and PSS is polystyrene sulfonate. The use of negatively charged and positively charged ionomers advantageously makes it particularly easy to produce the cellulosic material. The ionomers can be easily dissolved in water and thus fed to the process of making the cellulosic material, which is also water-based. By crosslinking the ionomers following preparation of the cellulosic material, the resistivity of the cellulosic material can be lowered. The ionomers polymerize and form in the cellulosic material an electrically conductive network, which is responsible for the reduction of the specific resistance. In particular, the mentioned ionomers can also be used to coat already mentioned semiconducting or non-conducting nanoparticles.

According to the filed with the file number after the date of this application DE 10 2009 033 267.7 For example, the nanocomposite can also be impregnated with semiconducting nanoparticles which are at least partially made of BNNT and distributed in the cellulose or a polymer. To increase the effective conductivity of at least part of the BNNT distributed in the insulating material, a doping of this BNNT with suitable dopants or a coating with metals or doped semiconductors is provided on the BNNT. The concentration of BNNT can be chosen so that the nanocomposite has a specific Conductivity ρ has the order of 10 ¹² Ωm. According to this variant, no conductive polymers are used as a sheathing of the BNNT.

Doping can be achieved by modifying the BNNT by adding suitable dopants such that the dopant atoms form electronic states that will make the BNNT a p-conductor (ie, electronic states that capture electrons from the valence band edge ) or to an n-conductor (ie, reaching electronic states that emit electrons by thermal excitation across the conduction band edge). As a dopant for a p-doping, for example Be comes into question, as a dopant for n-doping Si comes into question. Such doping of the BNNT can be done in situ, during the growth of the BNNT z. B. from the gas or liquid phase, the dopant atoms are incorporated. It is also possible to carry out the doping in a further step after the growth of the BNNT, wherein the dopants are typically taken up by the BNNT under the influence of a heat treatment. By introducing the dopants into the BNNT, the resistivity can be lowered to values typical for doped semiconductors between 0.1 and 1000 Ωcm.

According to the filed with the file number after the date of this application DE 10 2009 033 268.5 For example, the nanocomposite made of cellulosic material can also be impregnated with semiconducting nanoparticles, wherein doping of these nanoparticles with dopants is also provided to increase the effective conductivity of at least part of the nanoparticles distributed in the insulating material. The use of the semiconducting nanoparticles, in particular BNNT, has the advantage that low filler contents of at most 5% by volume, preferably even at most 2% by volume, in the insulating material are sufficient to cause percolation of the nanoparticles and thus increase the electrical conductivity of the nanocomposite.

The object of the invention is to improve an initially specified wiring to the effect that it has a higher dielectric strength and a greater structural design freedom for the construction of the cable bushing.

This object is achieved with the above-mentioned cable bushing according to the invention characterized in that the envelope is designed as a composite consisting of a treated cellulosic material. The cellulosic material is treated according to the invention by distributing in this particle a lower specific resistance in a concentration above the percolation threshold compared to the specific resistance ρ _{p of} the treated cellulosic material. Alternatively or additionally, it may be provided that in the cellulosic material a coherent network of a conductive polymer with a lower resistivity than the specific resistance ρ _{p of} the untreated cellulose material pervades the composite. The addition of particles or the provision of a network of a conductive polymer in a cellulose material in the manner indicated has the effect of reducing the specific resistance of the composite thus produced in comparison to untreated cellulose material. As a result, the specific resistance of the composite is matched to that of transformer oil, so that a load on the insulating section can be reduced evenly when subjected to a DC voltage across the individual elements of the insulating section. Specifically, the voltage drop across the cellulosic material is lower, so that the transformer oil is loaded to a greater extent. Here, a reserve is used according to the invention, which is available anyway. Thus, the structural scope for the design of cellulose barriers, in particular the envelope of the passage element is advantageously increased advantageous.

The described, for the invention essential effect of a relief of the cellulosic material by the voltage drop takes place to a greater extent on the transformer oil can be used advantageously good if the specific resistance ρ _{comp of} the composite is not more than 5 times 10 ¹³ Ωm. Advantageously, in order to utilize this effect, it is also possible to set a specific resistance ρ _{comp of} the composite which is 1 to 20 times the specific resistance ρ _{o of} the transformer oil. It can be provided particularly advantageously that the specific resistance ρ _{comp of} the composite corresponds, on the order of magnitude, to the specific resistance of transformer oil. By order of magnitude, it is meant that the specific resistance ρ _{comp of} the composite differs by at most an order of magnitude from that of the transformer oil (ie at most by a factor of 10).

The specific resistances ρ _o , ρ _p and ρ _comp in the context of this invention should each be measured at room temperatures and a prevailing reference field strength of 1 kV / mm. Under these conditions, the resistivity ρ _{o is} between 10 ¹² and 10 ¹³ Ωm. It should be noted, however, that the specific resistance ρ _o of transformer oil is rather reduced in the case of an inventive heavier load due to the voltage drop across the transformer oil.

In the embodiments described in more detail below, it is therefore assumed that a specific resistance ρ _o in the transformer oil of 10 ¹² Ωm.

According to a further advantageous embodiment of the invention, it is provided that the specific resistance of adjacent, forming the envelope layer layers is graded, wherein the layer layer or the layer layers with the lowest resistivity adjacent to the electrode tube or the conductor bolt. In other words, the cladding is constructed from several layers which differ in their electrical properties. It is thus possible to change the resistivity in the enclosure in stages, it being advantageous if the resistivity in the enclosure to the passageway decreases. As a result, the effect of a field grading in the area near the passage element can be used more. In particular, it can also be provided that the specific resistance of the casing is lowered to a region greater than or equal to the specific resistance of the transformer oil only at the surface of the casing which forms an interface with the surrounding transformer oil, while the specific resistance inside the casing Passage element is further lowered towards. As a result, load peaks in the wrapping material can be reduced near the passage element.

Furthermore, it is advantageous if the wrapping consists of a paper winding with several winding layers, wherein the paper winding is wound around the electrode tube or the conductor bolt. As a result, a particularly simple production of the envelope is advantageously possible. This is wrapped around the transmission element by rotating it around its center axis. It should be noted that a winding layer is dependent on the paper thickness, while the already mentioned layer layer is dependent on which region should be equipped with which specific resistance. When winding with paper, layers of different resistivity can be made by using different papers. However, a winding layer is generally much thinner (because of the paper thickness) as a layer layer. A layer layer is thus produced by winding a plurality of winding layers.

Furthermore, it is advantageous if the thickness s of the covering is reduced in comparison with the required thickness when using the relevant untreated cellulose material instead of the composite. This is an advantageous possibility of how the structural freedom of design, which results from the reduction of the specific resistance of the envelope, can be exploited. Due to a smaller thickness of the envelope, the space required for the line feedthrough is advantageously reduced. Due to the reduced specific resistance, the dielectric strength of the cladding remains the same.

Furthermore, it is advantageous if solid barriers are provided around the casing to form gaps (ie gaps) for transformer oil between the solids barriers with each other and with respect to the casing. This results in an alternating sequence of transformer oil and cellulosic material. This sequence gives the Isolierstrecke. It is particularly advantageous if the solids barriers also consist of the treated cellulosic material, ie. H. are reduced in their specific resistance. As a result, the structural freedom of design can advantageously be extended even more by, for example, providing solid barriers having a reduced wall thickness. Here, a wall thickness of 1 mm should not be undercut, since this is a constructive design limit. Namely, the solid barriers must have sufficient mechanical stability. Preferably, wall thicknesses of 1 to 3 mm can be provided.

It is also possible that the solid barriers are equipped with graded electrical resistors, as has already been described for the enclosure. The specific resistance increases with increasing distance of the solids barrier to the passage element. The graduated setting of different specific resistances of solid barriers as well as layer layers in the enclosure has the advantage that the specific resistance can be adapted to the respectively locally present field strength of the electric field surrounding the transmission.

Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same reference numerals in the individual figures and will only be explained several times to the extent that differences arise between the individual figures. Show it:

1 schematically a section of an embodiment of an insulating section for a passage and

2 a further embodiment of a cable feedthrough in a schematic longitudinal section.

An electrical insulation route 18 according to 1 generally consists of several layers cellulosic material 19 between which are oil layers 20 can lie. The insulating section starts at the metallic surface 11 a component to be isolated 12 , which may be formed for example by a tube of a non-illustrated implementation for an electrical line HVDC component from the associated housing. Also the cellulosic material 19 is soaked in oil, which is in 1 not shown in detail. This is in 1 an impregnation within the cellulosic material 11 to recognize. The according to 1 insulation shown surrounds, for example, in a transformer that there used for use Elektodenrohr 21 a cable bushing for the boiler wall.

The electrical insulation, for example, of a transformer must prevent electrical breakdown in the case of operation in the presence of an AC voltage in the area of the bushings. In this case, the isolation behavior of the insulation depends on the permittivity of the components of the insulation. For oil, the permittivity ε _{o is} approximately 2, for the cellulosic material ε _p at 4. When the insulation is subjected to an alternating voltage, the load on the individual insulation components results in the voltage U _o applied to the oil being approximately twice as high such as the voltage applied to the cellulosic material U. It uses a nanocomposite in which the cellulosic material 19 impregnated according to the invention, so influences the impregnation 11 the stress distribution in the insulation _according to the invention not, since the permittivity ε _{BNNT is} also approximately at 4 and therefore the permittivity ε _{comp of} the impregnated cellulosic material is also about 4. Thus, even with the insulation according to the invention, the voltage U _o applied to the oil is approximately twice as great as the voltage U _comp applied to the nanocomposite (cellulosic material).

At the same time, the breakdown strength of the insulation in the case of HVDC components when DC voltages are present is also important. The distribution of the applied voltage to the individual insulation components is then no longer dependent on the permittivity, but on the resistivity of the individual components. The specific resistance ρ _o of oil is between 10 ¹³ and 10 ¹² Ωm. Considering that according to the invention, a greater part of the voltage drop to relieve the cellulosic material in the oil is to take place and that the specific resistance of the oil decreases when a voltage is applied, it is rather, as in 1 shown to start from a resistivity ρ _o of 10 ¹² Ωm. In contrast, ρ _p of cellulose material is three orders of magnitude higher and is 10 ¹⁵ square meters. This has the effect that, when DC voltage is present, the voltage across the oil U _{o is} one-thousandth (assuming ρ _o = 10 ¹³ Ωm at least one hundredth to one hundredfold) of the stress on the cellulosic material U _p . This imbalance involves the risk that breakdown of the insulation material with a DC voltage leads to breakdowns in the cellulosic material and the electrical insulation fails.

The invention in the cellulosic material 19 introduced impregnation 11 can z. B. from BNNT and is adjusted by a suitable coating of BNNT from PEDOT: PSS and possibly by an additional doping of the BNNT with dopants with their resistivity (between 0.1 and 1000 Ωcm) that the specific resistance of the cellulose material ρ _{p is} lowered. This is also possible by the sole use of PEDOT: PSS or the sole use of BNNT. This makes it possible to set a specific conductivity ρ _comp for the composite according to the invention, which is approximated to the specific resistance ρ _o and ideally corresponds approximately to this. With a specific resistance ρ _comp of at most 5 times 10 ¹³ Ωm, the voltage U _o applied to the oil is of the order of magnitude in the region of the voltage U _comp applied to the composite, so that a balanced voltage profile is established in the insulation. As a result, the dielectric strength of the insulation is advantageously improved, since the load on the cellulosic material is noticeably reduced.

A routing according to 2 has a lead tube as an electrode tube 21 on. As an alternative to this embodiment is beyond the line of symmetry 22 a ladder bolt 23 represented, which can also act as a passage element. While the electrode tube 21 serves to pass an HVDC line, which is not shown in detail, is when using a Leiterbolzens 23 the HVDC cable at the front ends 24 electrically conductive, so that the conductor bolt 23 itself part of the HVDC line. Regardless of whether the ladder bolt 23 or the electrode tube 21 is used, so is on the conductive surface 25 of this component a cladding 26 made of a cellulosic material. This envelope consists of several layers 27 consisting of windings of a paper. These have different specific resistances.

Concentrically arranged around the casing are still several solid barriers 28 . 28i made from pressboard, which also consists of a cellulosic material with reduced specific resistance. Between the solid barriers between each other and between the innermost solid barrier 28i and the serving 26 are spaces in the form of columns 32 provided, which are filled in a manner not shown with a transformer oil. The solid barriers and the cladding give together with a shield electrode 30 the insulating section for the HVDC line feedthrough.

The shield electrode 30 serves to accommodate the HGÜ line, not shown, which is laid loop-shaped due to the realization of an axial compensation within the screen electrode. The shield electrode itself is also coated with a cellulosic material 31 Mistake. Also, this layer may consist of a paper wrap or, for example, from a molded body of pressboard. Also for the shift 31 It is considered that a use of the cellulosic material according to the invention with reduced resistivity is particularly advantageous.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 285895 A1 [0002]
• DE 102005021225 A1 [0002]
• US 4521450 [0004]
• WO 2004/038735 A1 [0005]
• US 2007/0199729 A1 [0005]
• WO 2006/122736 A1 [0007]
• WO 2006/131011 A1 [0008]
• DE 102010041630 [0010]
• DE 102007018540 A1 [0010]
• DE 102010041635 [0011]
• DE 102009033267 [0012]
• DE 102009033268 [0014]

Claims (9)

Cable bushing for the boiler wall of an HVDC component, comprising • an electrode tube ( 21 ) or a conductor bolt ( 23 ) with a conductive surface and • an envelope ( 26 ) of a cellulosic material, in particular paper, the electrode tube ( 21 ) or the conductor bolt ( 23 ) completely encloses, characterized in that the wrapping ( 26 ) is made of a composite consisting of a treated cellulosic material ( 19 ), In which particles are distributed with a resistivity lower than the percolation threshold compared to the specific resistance ρ _{p of} the untreated cellulose material, and / or in which a contiguous network of a conductive polymer with a specific resistance ρ _p of the untreated cellulosic material lower resistivity pervades the composite. Cable bushing according to claim 1, characterized in that the specific resistance ρ _{comp of} the composite is at least on the surface of the casing ( 26 ) is at most 5 times 10 ¹³ Ωm. Cable bushing according to claim 2, characterized in that the specific resistance ρ _{comp of} the composite is at least at the surface of the casing ( 26 ) is one to twenty times the specific resistance ρ _{o of} the transformer oil Cable bushing according to claim 2, characterized in that the specific resistance ρ _{comp of} the composite is at least at the surface of the casing ( 26 ) corresponds in order of magnitude to the specific resistance of transformer oil. Cable feedthrough according to one of the preceding claims, characterized in that the specific resistance of neighboring envelopes ( 26 ) forming layer layers ( 27 ), wherein the layer layer or the layer layers with the lowest specific resistance to the electrode tube ( 21 ) or the conductor bolt ( 23 ). Cable bushing according to one of the preceding claims, characterized in that the sheath ( 26 ) consists of a paper winding with several winding layers, wherein the paper wrap around the electrode tube ( 21 ) or the conductor bolt ( 23 ) is wound. Cable bushing according to one of the preceding claims, characterized in that the thickness s of the envelope ( 26 ) is reduced compared to the required thickness using the respective untreated cellulose material instead of the composite. Cable bushing according to one of the preceding claims, characterized in that around the envelope ( 26 ) Solid barriers ( 28 . 28i ) forming gaps for transformer oil between the solid barriers to each other and to the envelope ( 26 ) are provided. Cable bushing according to claim 8, characterized in that the solid barriers +16 also from the treated cellulose material ( 19 ) consist.

Images